mulch – Page 3 – The Garden Professors™

Why won’t landscapers use mulch?

A few weeks ago I was in Olympia (it misses you Bert!) reviewing grant applications. As I tend to do whenever I have time and my camera, I set out in search of gardening goofs that evening. Here’s the edge of a relatively new commercial site I discovered:

OK, not too bad so far. We’ve got a nice stone mulch next to the curb, then a lovely groundcover, in flower, that also functions as a living mulch. But what’s that we see in the upper half of the photo?

Yes, it’s Canada thistle (Cirsium arvense), an aggressive perennial weed that spreads by stolons and can make dense monocultures of prickly nastiness. In fact, the front is already advancing on our little groundcover:

Had the landscapers continued with mulching the soil rather than leaving it bare, these thistle seeds might not have germinated. But for whatever reason, the bulk of the landscape was left bare:

I’m sorry, but this just looks ridiculous. There was some obvious care in laying the stone mulch and groundcover, but then the landscaper seems to have run out of time and/or money and just plopped in some bulbs and corms. It reminds me of a birthday cake.

I don’t understand the rationale behind this. Was this a real design? Did the client run out of money? Or (as the more cynical side of me wonders) was this done deliberately to create a high maintenance landscape requiring lots of weeding in the future?

Thoughts?

Pigmented Mulch in Paradise

Just back from a quick vacation to Little Cayman island. Truly a dot on the map – the whole island is about 7 miles long and a mile wide. Only 150 locals and a couple hundred tourists are on island at any one time. It’s beyond laid back, with few attractions other than the resident iguanas and red-footed boobies (booby jokes abound).

Airport terminal/post office/fire station.

The big draw is diving – LC is the home to Bloody Bay Wall, one of the most famous dives in the Caribbean. The reef drops off like a sheer cliff, from 40-60′ to more than 1000′.

All the action is underwater!
(Let me know if you want to see more slightly blurry diving photos.)

“Fascinating, Holly. But what does this have to do with painted mulch?”

The extent of the landscaping for most yards: conch shells arranged in interesting designs and/or piles. But as we pedaled past a rather upscale condo, I came to a screeching halt. A gorgeous Bismarckia nobilis had caught my eye, but then I saw what was under it. Egad.

Everything comes to Little Cayman by a weekly barge or little prop plane and is wildly expensive. Four-pack of batteries? $15. A six-pack of beer is $20. TWENTY DOLLARS!!!

So, good readers, what we have here is possibly the most expensive mulch on the face of the earth. I can’t even imagine.

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How to get rid of your lawn

With increasing interest in reducing monocultural swaths of turf, summer water consumption, and the drudgery of mowing, many people are eliminating part or all of their lawns. We did this at home some years ago and can attest to the tangible benefit of reduced water bills during our dry summer months.

The question I often get is – how? Do you dig up the turf and throw it out, then fill in with topsoil? Or do you cut it, flip it, and then plant on top of it? Or do you cover it up with cardboard to kill it?

We’ve tried all of these methods over the years (except sheet mulch, because you already know what I think about that). What I now recommend is the easiest, cheapest, and most effective way to both remove turf and protect the soil. Here it is in four easy steps:

1) Mow your lawn as close to the ground as possible. Scalp it. If you can wait until it’s not actively growing (summer here in the west), that’s even better. Don’t water it!

2) Cover it up with – yes, you guessed it – a really thick layer of arborist wood chips. They need to be at least 8″ thick and can be as much as 12-18″ deep without negative effects. They will settle quickly, so you do need to put enough down to maintain a 6-8″ depth after a few weeks. The depth is important to suppress the turf as well as any persistant weeds (like those you can see in the above photo).

3) Wait. Turf decomposition will depend on temperature and water availability – warm and moist conditions are optimal. After 2-4 weeks, pull part of the mulch back and check out what’s underneath. When it’s easy enough to dig through, then you can…

4) Plant. Be sure to move the mulch aside and plant into the soil. Replace the mulch to cover the disturbed soil and keep the weeds down. It only needs to be 3-4″ deep at this point.

It’s that easy.

Is Black The New Brown?

Mulch is always an interesting point of discussion as well as the topic of several past GP posts. But I honestly can’t recall if we’ve covered dyed mulch, and can’t search the site, so here goes.

I recently received a request for information from Debbie Dillon, a fine Urban Horticulturist with Virginia Cooperative Extension. She noted the increased use of dyed mulch in the Northern Virginia area, and has been fielding questions from both landscape designers and homeowners regarding the safety of said mulch and the potential for harmful effects on plants. Black seems to be a fave color of late.

All I could offer her at the time was “Bleccch, I really don’t care for it” and a promise to investigate further. Armed with a bit of spare time and Google – here’s what [little] I’ve found out.

There are several products out there, such as Solarfast MCH and Mulch Magic. They’re used commercially on bulk mulch and are also available to the homeowner without restriction. From the Solarfast website – “Solarfast MCH is a colorant used to restore faded mulch back to its original color. It is environmentally friendly and does not contain hazardous chemicals, heavy metals or other ingredients that are known to be harmful to the environment.”

Is it safe?

The MSDS (Material Safety Data Sheet) for Solarfast was incomplete – it did not list components. The MSDS for Mulch Magic indicates the black contains carbon black, red contains iron oxide, and brown contains diethylene glycol monobutyl ether (as well as carbon black and iron oxide). The composition beyond that (carriers, surfactants, etc.), was not noted. Diethylene glycol monobutyl ether is a fairly common solvent for paints and inks with purportedly low environmental toxicity, but can irritate skin and eyes. Carbon black can be made from various sources but is basically a petroleum product, used in laser printer and photocopier toner as well as the manufacture of reinforced rubber (i.e. tires). Most concerns are related to worker inhalation at the point of manufacture. Iron oxide is, well, oxidized iron, and has been used as a pigment for quite a while (i.e. cave paintings at Lascaux, Bob Ross, etc.).

What about the plants?

There are many, many studies on pigmented film mulches (usually polyethylene) in fruit and vegetable production. Certain colors can alter plant growth and processes, such as flowering and fruiting, stem length, etc., but I couldn’t find a thing regarding dyed, wood-product mulch. Issues of concern might be that the dye is disguising the composition of the mulch. Apparently dyes are frequently used on “pallet mulch” – shredded pallets, usually made from softwood. Another concern might be the increase in root-zone temperature, especially from the use of heat-absorbing black pigments. Could soil temperatures warm to the point of causing a too-early bud break?

Is it aesthetically pleasing?

Apparently “yes”, to some, because there’s a market for it. What do you think?

This photo was taken in April at a local medical center (it was a rainy morning, pardon the low light). The fairly typical commercial landscape surrounding the building is dotted with beds and trees freshly mulched in black. Note the classic mulch “volcano” in the background. No sir, I don’t like it. But that’s just me.

Toxicity information on compounds noted available at the International Agency for Research on Cancer (IARC) – Summaries & Evaluations, http://www.inchem.org/

Permaculture – more concerns

One of the gardening topics I’ve researched extensively is the use of landscape mulches. (You can read a literature review I did a few years ago here.) So I was more than a little frustrated to see one of the worst mulching techniques – sheet mulching – extolled in the book Gaia’s Garden (pp. 85-90).

Sheet mulches, like newspaper and cardboard, can be used successfully as a temporary weed control measure (i.e. a few weeks before planting a vegetable garden). Long term, they are not a sustainable choice and often cause more damage to the system than the presence of weeds.

The two-dimensional structure of sheet mulches functions as a barrier to not only weeds but to the movement of air and water as well. While this may initially increase soil water retention since evaporation is reduced, over the long term they will create soils that are unnaturally dry. This condition is worsened on low-maintenance sites,where neglected sheet mulches easily dry out, causing rainfall or irrigation water to sheet away rather than percolate through.

In contrast, wet, poorly drained soils will become even more so as layers of moist paper or cardboard restrict evaporation and aeration. Moreover, this condition encourages root growth on top of the sheet mulch, which can injure desirable plants when and if the sheet mulch is removed.

There are other disadvantages as well. Exposed newspaper and cardboard mulches are easily dislodged by the wind, animals and pedestrians and often provide food for termites and shelter for rodents such as voles. Combined with a somewhat marginal ability to control weeds compared to other organic mulches, sheet mulches are arguably one of the least attractive or effective choices for a sustainable landscape.

Sheet mulching proponents will argue that newspaper and cardboard are only part of the mulch structure – that organic materials such as compost and wood chips need to be added as well. To which I respond – then why bother with the sheet mulch? Why not just use deep layers of coarse organic materials? That’s exactly what forest duff layers consist of. It’s been repeatedly demonstrated that thick layers of coarse organic materials are the best and most natural choices for mulching. (See, for instance, my Ecological Restoration article on using a foot of arborist wood chips to suppress blackberry and enhance native plantings. )

The appeal of sheet mulching is its formulaic structure and logical approach – it’s like making lasagna (the name of yet another nonscientific approach to mulching). Unfortunately, sheet mulching is neither natural nor particularly effective.

Building healthy soils?

I love living in Seattle…but I’m getting increasingly impatient with the City’s “Building Healthy Soils” propaganda. For years I’ve questioned their recommendation to perpetually amend landscape soil with organic material to no avail. Let’s see what you all think of their “fact sheet” (which you can read here in its entirety).

“The best way to improve the soil is to add plenty of compost or other organic matter throughout the entire planting area before planting. Thoroughly mixing these materials deep into the soil helps provide water, air and nutrients to plant roots.”

Hmm. No mention of how to determine IF your soil needs improving; without a soil test, you have no idea what your baseline organic matter level is.

But perhaps this recommendation is only for vegetable gardens and annual beds? Nope. In the next paragraph, we’re told to “Mix in organic material before planting lawns, perennials, trees and shrubs.” We’re given helpful how-to instructions: “Use a shovel or digging fork to mix amendments into the top 6 to 12 inches of soil. It is important to amend the entire planting bed — not just small holes for each plant. When planting individual trees and shrubs in lawns or existing beds, amend an area at least 3 feet wide, or 3 to 5 times as wide as root balls over 12 inches in diameter. Rototill large areas where digging is impractical.”

Now we’ve got a serious problem. This practice is recommended for existing beds. Not only will extensive digging or rototilling destroy any soil structure you might have, it will also take out the roots of any desirable plants in the vicinity).

But let’s continue to ignore reality and go on to the annual recommendations for adding compost to soils.
“Clay soils: 16 cu. feet (.6 cu. yard) = 2 inch layer of compost for new gardens. Use 1 inch per year in established gardens.”
“Sandy soils: 24 cu. feet (.9 cu. yard) = 3 inch layer of compost for new gardens. Use 1 – 2 inches per year in established gardens.”

Is the compost used as a mulch in these existing gardens? No – the guidelines are prefaced with this instruction: “Gardens: mix compost to 10- to 12-inch depth.” (Can’t say this does much for promoting root growth either.)

This document shows a breathtaking lack of understanding of how landscapes function, especially over the long term. It takes an agricultural practice (annual organic amendment of crop fields) and misapplies it to permanent landscapes. It is devoid of the research which continues to show that improper soil amendment can cause serious problems such as soil subsidence, perched water tables, and nutrient overloads. This last point is especially important to anyone living near aquatic ecosystems, since excess nutrients always end up in the water.

Before you plant this year, find out what your soil needs before amending it. And remember that mulching is the natural (and sustainable) way to add organic matter to the soil.

Will cocoa mulch kill my dog?

Recently I was asked to comment about a rash of e-mails floating around cyber-space concerning the toxicity to dogs of mulch made from crushed cocoa bean hulls. Cocoa mulch is by-product of cocoa production. The dark brown mulch is aesthetically and aromatically pleasing, giving the garden a rich, chocolately scent. Since theobromine, a naturally occurring compound in chocolate is toxic to dogs, the internet is now filled with cyber-legends of dogs eating cocoa mulch and keeling over dead.

According to an article published in the Journal of the American Veterinary Medical Association (JAVM June 1, 2006 p. 1644), cocoa bean husks can contain up to 2.98% theobromine. The JAVN article state “no reports of lethal toxicosis from ingesting this mulch have been filed with the ASPCA Poison Control Center this year (2006). In 2004 and 2005, 16 reports of single exposure to the mulch were received, none resulting in death.”

The ASPCA posts this comment regarding cocoa mulch on its website:
“Dogs consuming enough cocoa bean shell mulch could potentially develop signs similar to that of chocolate poisoning, including vomiting and diarrhea. In cases where very large amounts of mulch have been consumed, muscle tremors and other more serious neurological signs could occur. To date, the ASPCA Animal Poison Control Center has not received any cases involving animal deaths due to cocoa mulch ingestion. One key point to remember is that some dogs, particularly those with indiscriminate eating habits, can be attracted to any organic matter. Therefore, if you have a dog with such eating habits, it is important you do not leave him unsupervised or allow him into areas where such materials are being used.”

It should be noted that processed cocoa mulch may contain much lower concentrations and some manufacturers market cocoa mulch that is ‘Pet safe’. Consumers should look for products that are tested and certified theobromine free.

As always, I stand by my recommendation to use locally processed wood products such as ground hardwood bark and ground pine bark. Plants grow well in these mulches, which are typically among the most cost-effective and natural looking (to me, at least) mulches available, and they are renewable and help support your local economy.

Should I boycott cypress mulch?

It’s hard to think of mulch as a controversial topic but, as with most things these days, we find people on both sides of an issue. And, as with most things these days, some of opinions are based on substance, others are not. In the southern U.S. some environmental groups are advocating a boycott of cypress mulch.

Cypress mulch is derived from baldcypress and pond cypress, which grow in ecologically sensitive wetlands in the Southeast. Cypress wood is highly valued for is natural decay resistance. Florida and Louisiana are the leading states for cypress harvesting for timber and other products. In Louisiana it is unclear if cypress is logged solely for mulch but cypress harvesting for mulch does occur in Florida. According to Dr. Jim Chambers, professor of Forestry at Louisiana State University and Chair of a governor’s science panel on forested wetlands in Louisiana, cypress mulch production is a sensitive issue. “Many of our cypress-tupelo forests are in a severe state of decline. As you can imagine, these forests are very important to south Louisiana for many reasons. Areas permanently flooded, areas that are flooded for substantial parts of the growing season, and areas subjected to salt water input cannot regenerate. The amount of forested areas with these conditions continues to increase as subsidence increases, coastal wetlands are eroded by storms and human impacts on hydrology continue to degrade many sites.”

The inability to regenerate new stands of cypress is an important concern and calls into question the sustainability of cypress harvesting on these sites. Chambers is working with environmental groups and others to develop a process to certify that mulch is produced from sustainable forest harvest operations

Another issue related to cypress mulch is a claim that is circulating in parts of Michigan (and perhaps elsewhere) that cypress mulch is linked to cancer. I conducted a search of the National Library of Medicine and National Institutes of Health literature database (www.pubmed.gov) on ‘cypress’ and ‘cancer’. The only hits I found were related to studies looking at falsecypress (Chamacyparis) extracts for anti-cancer properties, similar to taxol. The claims of cypress mulch and cancer may be an amalgam of the environmental concerns over cypress harvesting discussed above and concerns over use of mulch derived from CCA (chromated copper arsenate) treated wood, which is used for decking and other uses similar to cypress. Research has shown that leachate from mulch containing CCA treated wood can have elevated levels of arsenic and metals above established health standards.

We all know Linda’s fondness for wood chips as mulch. My personal favorite is ground red pine bark for its durability and natural appearance. The key is to look for renewable mulch products that are locally sourced.

Wonderful wood chips

I’m in love…with arborist wood chips. These are not your beauty barks or other packaged mulches, but the chipped branches and leaves fresh from the tree crews. It’s a great way to keep this resource out of the landfill – and don’t even get me started about using this great mulch material for a “biofuel!”

I’ve written about wood chip mulches a lot, but thought today I would post some photos to show you how well they work in suppressing weeds and promoting growth in restoration sites. We published a paper on this in 2005, though we’ve been using them in ornamental and restoration landscapes for about 10 years.

Here’s a recent project: a wetland buffer enhancement was being installed in an area that was covered in Scot’s broom (Cytisus scoparius) and blackberry (Rubus discolor):

We had a brush cutter mow it to the ground, then put a foot of wood chips down. Later, we planted poplar, ash, willow and alder on the site:

We had to keep records, both written and photographic, for the county who monitors wetland projects. So we took photos every year at the same points for comparative purposes. Here’s what part of the site looked like immediately after planting and then after 5 years:

That’s not to say that we haven’t had to battle resurgent blackberries. They migrate over from the wetland itself (which we can’t touch) and tip root. But the increasing shade and competition from the trees has weakened their ability to take over, and the Scot’s broom has been gone for years.

So that’s one reason I love wood chips. I’ll do a follow up some week showing how they can be used in the home landscape.

Rubber mulch rubs me the wrong way

I’ve been receiving a lot of questions about rubber mulch lately. For those of you not familiar with the product, it consists of shredded tires that can be dyed and used on ornamental landscapes or under playground equipment. In fact, the Obamas had this material installed underneath their children’s play structure at the White House. It seems an ideal way to recycle the 290 million scrap tires we generate annually.

But is it?

It’s not effective: One of the main reasons we use mulch is to suppress weeds. Research has demonstrated that organic mulches such as wood chips, straw, and fiber mats control weeds better than rubber mulch.

It burns: You’ve heard stories about piles of scrap tires catching fire and burning for weeks. Well, those same flammable compounds are in rubber mulch, too. When compared to other mulch types, rubber mulch is the most difficult to extinguish once ignited. In fact, some parks and playgrounds no longer use rubber mulch or rubberized surfaces because vandals have figured out that rubber fires cause a LOT of damage.

It breaks down: Although sales literature would have you believe otherwise, rubber is broken down by microbes like any other organic product. Specialized bacterial and fungal species can use rubber as their sole food source. In the degradation process, chemicals in the tires can leach into the surrounding soil or water.

It’s toxic: Research has shown that rubber leachate from car tires can kill entire aquatic communities of algae, zooplankton, snails, and fish. While part of this toxicity may be from the heavy metals (like chromium and zinc) found in tires, it’s also from the chemicals used in making tires. These include 2-mercaptobenzothiazole and polyaromatic hydrocarbons, both known to be hazardous to human and environmental health.

It’s not fun to be around: When rubber mulch gets hot, it stinks. And it can burn your feet. Yuck.

The EPA’s website says this about scrap tires: “Illegal tire dumping pollutes ravines, woods, deserts, and empty lots. For these reasons, most states have passed scrap tire regulations requiring proper management.” So if we have legal tire dumping (in the form of rubber mulch), does that mean it doesn’t pollute anymore?

(You can read a longer discussion on rubber mulches here.)